Blasting machine with overvoltage and undervoltage protection for the energy storage capacitor

ABSTRACT

An electrical system for firing an explosive bridge wire device or the like which includes a battery powered blocking oscillator to charge a storage capacitor, a circuit controlling the maximum energy to be contained in the storage capacitor, and a circuit that determines the minimum energy in the storage capacitor before the storage capacitor can be discharged into one or more explosive bridge wire devices or the like.

iliieili Sates Patent McKeown et al.

BLASTING MACHINE WITH OVERVOLTAGE AND UNDERVOLTAGE PROTECTION FOR THEENERGY STORAGE CAPACITOR Inventors: James E. McKeown, Sdriey;rrlrving E.Linkroum, Hancock; Earl M. Phinney, Oneonta, all of N.Y.

Assignee: The 4Bendix Corporation, Southfield,

Mich.

Filed: Nov. 23, 1971 Appl. No.: 201,525

U.S. Cl. ..320/1, 307/108, 317/80, 331/1 l l Int. Cl. ..H03k 3/30, H02m3/22 Field of Search ..320/1; 331/111; 317/80; 307/108 IHT 1451March 20,1973 [56"] References Cited UNrrED STATES PATENTS PrimaryExaminer-Bernard Konick Assistant Examiner-Stuart Hecker Attorney-Raymond J. Eifler et al.

[5 7] ABSTRACT An electrical system for firing an explosive bridge wiredevice or the like which includes a battery powered blocking oscillatorto charge a storage capacitor, a circuit controlling the maximum energyto be contained in the storage capacitor, and a circuit that determinesthe minimum energy in the storage capacitor before the storage capacitorcan be discharged into one or more explosive bridge wire devices or thelike.

8 Claims, 2 Drawing Figures PATENTEUMARzolS SHEET 2 UF 2 BLASTINGMACHINE WITH O VERVOLTAGE AND UNDERVOLTAGE PROTECTION FOR THE ENERGYSTORAGE CAPACITOR BACKGROUND OF THE INVENTION This invention relates toan improved blasting machine for detonating blasting caps or the like.The invention is more particularly related to a battery powered blastingmachine of the capacitor discharge type.

Basically, electrical systems for firing explosive devices include asource of power such as a battery, an oscillator, a transformerresponsive to the oscillator for stepping up the pulses therefrom, astorage capacitor which is charged by the pulses from the transformer,and a trigger circuit which allows the energy stored in the capacitor todischarge to fire an explosive device. The energy stored in thecapacitor is discharged through the explosive device by means of atriggering circuit which may be operated automatically or manually.Examples of such blasting devices may be found in U.S. Pat. No.3,417,306 entitled Regulated Voltage Capacitor Discharge Circuit to .l.L. Knak, issued Dec'. 17, 1968; and U.S. Pat. No. 3,275,884 entitledElectrical Apparatus for Generating Current Pulses to L. H. Segall etal., issued Sept. 27, 1966.

In certain blasting operations such as those performed in tunnels andshaft mining, it may be necessary to connect from as few as 1 blastingcap and as many as l50 blasting caps together in a parallel circuit.Parallel connections are used becausesuch connections permit rapidconnection ofthe blasting caps with minimal possibility of error. Toinsure that all the blasting caps are fired, the blasting machine mustalways deliver a given minimum energy each time it is fired, otherwiseall of the blasting caps may not be fired. Further, it is also importantthat the blasting machine does not deliver too much energy to theblasting caps, otherwise malfunction of some of the blasting caps mayoccur. Therefore, to insure that all blasting caps are fired, theblasting machine must always deliver an amount of energy in apredetermined energy range depending upon the number of blasting caps tobe fired.

Further, all too frequently, under heavy loading conditions, existingcharging circuits utilizing a transformer having a control winding(teritary) experience high frequency oscillations that affect theoperation of the circuit and, therefore, the maximum power that can betransferred to the load. The high frequency oscillations occur becausethe amount of feedback to the control winding that turns OFF the switchtransistor in series with the primary winding depends upon the voltageacross the secondary winding in parallel with the storage capacitor. Atlow magnitudes of charge on the loads on the storage capacitor, thefeedback to the control winding is frequently insufficient to overcome apositive bias on the switching transistor. Therefore, the switchingtransistor is OFF for very short intervals, hence high frequencyoscillations occur.

SUMMARY OF THE INVENTION This invention provides an improved blastingmachine that prevents low energy and high energy firing and is notsusceptible to spurious oscillations in the charging circuit thatadversely affects the operation of the machine. The invention is ablasting machine like.

In one embodiment of the invention, the blasting machine comprises: acapacitor; means for supplying electrical energy to the capacitor, saidmeans for supplying electrical energy comprising a battery, atransformer having a secondary winding and a primary winding connectedto the battery, a first diode means and the capacitor connected togetherin series across the secondary winding to store energy generated by thecurrent flowing through the primary winding, a solid state switchoscillator connected to the battery and the transformer to periodicallyinterrupt current flow from the battery through the primary winding, theoscillator including: a first transistor having collector and emitterterminals in series with the primary winding, 'the transistor havingalternate conductive and nonconductive intervals to periodicallyinterrupt the current flowing from the primary winding; a first voltagedivider network connected across the first transistor and the primarywinding, the first voltage divider network including second diode meansconnected to the junction between the primary winding and the firsttransistor to direct current from the winding in a predetermined manner;and a second voltage divider network connected across the battery, thesecond voltage divider network including a second transistor havingalternate conductive and nonconductive intervals to respectively controlthe conductive and nonconductive intervals of the first transistorwhereby the flow of current from the battery to the primary winding isperiodically interrupted causing current to flow in an oscillatorymanner through the primary winding; means for producing a plurality ofelectrical pulses when the capacitor has reached a first predeterminedenergy level; switching means for receiving the pulses, the switchingmeans operable to permit the discharge of the capacitor only during thepresence of the pulses, whereby the capacitor cannot be discharged belowthe predetermined energy level; and means for preventing the capacitorfrom exceeding a second predetermined energy level which is above thefirst predetermined energy level whereby the capacitor is prevented fromreaching energy levels above the second predetermined energy level.

Accordingly, it is an object of this invention to provide a batterypowered explosive ignition system that is not adversely affected by thenumber of devices which it detonates and which supplies energy to thedevices that falls within a predetermined energy range.

It is another object of this invention to provide an improved blastingmachine that is safe and reliable.

The above and other objects and features of this invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings and claims which form a part of i thisspecification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of ablasting machine that utilizes the principles of this invention.

FIG. 2 is a schematic diagram of a preferred embodiment of the circuitryfor a blasting machine shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG.1 illustrates a block diagram of a blasting machine which utilizes theprinciples of the invention. The basic portion of the system includes apower supply 1, an energy storage device 3, such as a capacitor forstoring energy supplied by the power supply 1, a pulse generator forgenerating pulses when the energy in the capacitor has reached apredetermined energy level, and a firing circuit 6 which permits thedischarge of the energy in the energy storage device 3 through the load8 which are the blasting caps or the like, when the trigger portion 7 ofthe firing circuit 6 receives pulses from the generator 5.

The power supply 1 may be either a.c. or d.c. and include the necessaryelectrical components for charging an energy storage device such as acapacitor.

The energy storage device 3 is preferably a capacitor. The voltageregulator 2 may be used in electrical circuit relationship with theenergy storage device 3 to assure that the energy stored in the energystorage device 33 does not exceed a predetermined voltage level. Theenergy storage circuit may include a switch that, in the ON positionpermits the energy storage device 3 to store energy, and in the OFFposition allows the energy storage device 3 to discharge so that noenergy remains in the energy storage device 3 when the blasting machineis not in use. The charge and discharge switch 9 may be either a singleswitch or multiple switches and may also be part of the firing circuit6.

A voltage indicator 4 may be used in combination with the pulsegenerator 5 to produce either visual or audible signals when the pulsegenerator 5 is generating pulses.

The firing circuit 6 includes a trigger 7 which allows the energystorage device 3 to discharge into the load 8. The trigger 7 may be agaseous conductor of the threeelectrode type wherein the triggerelectrode upon receiving pulses from the pulse generator 5 allows theremaining two electrodes which are in series with the energy storagedevice 3 to conduct, thereby allowing the energy stored in the device 3to discharge into the load 8. If it is desired that the blasting machinenot be automatically triggered, a switch may be located in series withthe pulse generator 5 so that when the voltage indicator 4 givesindication that pulses are present, manually operating the switch toclose the contacts will cause the trigger to conduct and discharge theenergy into the load.

FIG. 2 is a schematic diagram of a preferred embodiment ofa blastingmachine that utilizes a battery and an oscillator to charge the storagecapacitor which will be discharged to fire a blasting cap or otherexplosive bridge wire device or the like. The dotted lines outliningportions of the circuitry indicate the power supply l, the energystorage device 3, the voltage regulator circuit 2, the voltage indicator4 associated with the pulse generator, the pulse generator circuit 5,and the firing circuit 6.

The power supply 1 in this embodiment includes a battery 140, a switch9, a smoothing capacitor 130, and a transistorized oscillator circuit incombination with a step-up transformer 150, the output voltage of whichis applied to the energy storage means 3. In operation, the power supplycircuit 1 operates as follows:

A solid state switch oscillator is powered by a battery 140 or otherdirect current source. In one embodiment twelve one and one-half voltbatteries were used, which, because of the internal resistance thereof,provided a voltage between l0 to l2 volts. Connected across the battery140 is a capacitor 130 which, when charged, provides additional currentto the oscillator. A transformer 150 has its primary winding 101connected into the oscillator circuit and its secondary winding 151connected to a storage capacitor 153 through a diode 152 to store theenergy generated by the oscillator. The windings 101 and 151 oftransformer 150 are inductively coupled and wound and disposed in themanner indicated by the dots.

The solid state switch oscillator operates to intermittently interruptcurrent flow from the battery 140 through the primary winding 101 of thetransformer 150 and includes a first switching transistor 103, a firstvoltage divider network (110, 111, 112, 113), a second voltage dividernetwork (121, 122, 123), and first diode means (102, 104, 106) connectedbetween the first voltage divider network and the primary winding 101 ofthe transformer 150 to direct the flow of current to and from theprimary winding 101. The oscillator circuit shown is capable ofproducing oscillations in the range of 800 to 2,000 Hz.

The first voltage divider network includes a diode 110 and a pluralityof resistors 111, 112 and 113 connected together in series across theprimary winding 101 of the transformer and the first transistor 103.

The diode means that directs the current from the primary winding 101includes a first diode 102 connected by its anode terminal to thejunction between the primary winding 101 and the first transistor 103.To permit current to flow from the primary winding 101 when transistor103 is off, diodes 104 and 106 are connected in series with one anodeterminal connected to the junction between the primary winding 101 andthe first transistor 103 and one cathode terminal connected to thejunction between the second transistor 1 l2 and the third transistor113.

The second voltage divider network includes a transistor 121, a resistor122, and a resistor 123 connected together in series across the battery140. The base of the first transistor 121 is connected, for biasingpurposes, to the junction between 'the diode 110 and resistor lll of therst voltage divider network. The base of the first transistor 103 isconnected to the junction between resistors 122 and 123 to supply acurrent to the base of transistor 103 when the transistor 121 is in theconductive state.

The secondary winding 151 of the transformer 150 is connected to a diode152 and a capacitor 153. When the battery is l0 to l2 volts, the maximumcharge that can be obtained on capacitor 153 is about 7,000 to 8,000volts. However, voltages of this magnitude are not generally required inbattery powered explosive ignition systems, therefore, an additionalcircuit (not shown) may be added to limit the voltage across thecapacitor 153. The energy stored in the capacitor 153 is used for firingan explosive bridge wire device or the like.

In this embodiment, when a constant current source having an outputvoltage of about volts is used in lieu of the battery 140 and thecapacitor 153 is a 100 microfarad capacitor, the capacitor 153 can becharged to 200 joules within l0 seconds and to 400 joules withinseconds. Since batteries deteriorate with use, they are capable ofachieving the initial charged'energy previously stated, but tests revealthat when they are used to charge the capacitor 153 to 400 joules threetimes a day for 2l days, it would take a maximum of 7l seconds of chargetime to obtain 400 joules of energy at the capacitor 153. The minimumcharge time at the end of this period to obtain 400 joules of energy atthe capacitor 153 would be 49 seconds.

The energy storage means 3 includes a blocking diode 152 and storagecapacitor 153 in circuit relationship with the secondary winding 151 ofthe transformer 150. The discharge resistor 154 allows the energystorage in capacitor 153 to be discharged when the switch 9 in the powersupply l is in the OFF position.

The voltage regulator 2 which prevents the voltage on the capacitor153from exceeding a predetermined value includes a two-electrode sparkgap 160, a resistor 163, a capacitor 165, and a resistor 167. Thefunction of the regulator circuit is to drain excessive energy of thestorage capacitor 153 to prevent the storage capacitor from exceeding apredetermined upper energy limit. The spark gap 160 is a normallynonconducting device that conducts when the voltage across the devicehas reached a predetermined voltage. In'this instance, the breakdownvoltage of the spark discharge device 160 is chosen to be thepredetermined upper voltage limit desired across storage capacitor 153.ln operation, the voltage across the storage capacitor 153 appearsacross the spark gap 160. As the storage capacitor 153 is charged, thevoltage `across the spark gap 160 increases until the breakdown voltageof the device is reached. Thespark gap 160 then breaks down and conductscurrent to charge capacitor 165. The current through the spark device160 decreases as capacitor 165 becomes more fully charged. Eventuallythe current through the spark device 160 decreases to the point where itno longer will support an arc in the discharge device 160. The arcextinguishes and spark gap 160 ceases conduction. The charge on thecapacitor 165 is then discharged through resistor 167. As capacitor 165discharges, the voltage across the spark gap device 160 thereforeincreases, and if the voltage across the storage capacitor 153 is stillgreater than the breakdown voltage of the spark gap discharge device160, the discharge device 160 again conducts and the cycle is repeatedagain. If desired, a neon indicator light could be used in combinationwith this circuit to give an indication when the voltage regulator isoperating. The suggested method with respect to a voltage indicatingdevice would be to place a neon indicator light and resistor acrosscapacitor 165 which is responsive to the charging and discharging ofcapacitor 165.

The pulse generator circuit 5 includes a two-electrode spark dischargedevice 170, resistor 171, capacitor 177, resistor 173, and resistor 175.The voltage indicator light 4, such as a neon bulb, is in circuitrelationship with resistor 173 and 175 and is responsive to the chargingand discharging of capacitor 177. ln operation, the two-electrode sparkdischarge device 170 will remain in a nonconducting state as long as thevoltage on the storage capacitor 153 is less than the breakdown voltageof the spark discharge device 170. When the voltage on the storagecapacitor 153 exceeds the breakdown voltage of the discharge device 170,the device conducts allowing current to pass through resistor 1'71 tocharge capacitor 177. As the voltage on the capacitor 177 increases, thevoltage across the spark device decreases until the spark device 170returns to the original nonconducting state. At this time, capacitor 177then discharges through resistors 173 and 175 which further applies avoltage to the neon light 4 which gives an indication that this circuitis in operation. When the voltage across the spark discharge device 170again rises to the breakdown potential of this device, conduction beginsagain and the cycle repeats itself. Each time capacitor 177'is charged,voltage is applied to neon indicator light 4 through the resistordivider network 173, 175. The neon indicator light 4 stays lit until thevoltage across the light drops below the minimum sustaining voltage ofthe light 4. By this means, each time capacitor 177 is charged, there isa visible light pulse to signal the operator that the minimum voltagehas been reached and the blasting i machine may be tired. With thiscircuit, when the minimum voltage across the capacitor 153 is reachedand pulses are being generated by the pulse generator, pressing thefiring switch 181 in the firing circuit 6 will cause the pulses to betransmitted to the firing circuit.

The firing circuit 6 includes a three-electrode spark gap dischargedevice, a step-up transformer for raising the voltage of the pulsesreceived from the pulse generator 5 and applying them to the triggerelectrode of the spark discharge device 180, and a firing switch 181which permits the trigger pulses from the pulse generator 5 to betransmitted to the primary winding 185 of the step-up transformer. Forfurther details concerning the particular type of three-electrode sparkgap discharge device required for this circuit see U.S. Pat. Nos.3,187,215 entitled Spark Gap Device" to l. E. Linkroum issued June l,1965, and 3,229,146 entitled Spark Gap Device with a Control ElectrodeIntermediate the Main Electrodes" to l. E. Linkroum issued Jan. l l,l966. Inoperation, when the firing switch 181 is in the OFF position, nopulses are being supplied to the spark discharge gap 180 therebypreventing the firing of any blasting caps attached to the outputterminals 190. Further, the tiring switch 181 in the OFF position is yetin combination with the power switch 9 l in the OFF position to placethe discharge resistor 154 ditions are met, the output pulses of thepulse generator are transmitted to the primary winding 185 of thestep-up transformer where the pulses are stepped up to a higher voltageand applied to the trigger electrode of the spark gap discharge devicethrough resistor 183 thereby causing ionization within the spark gapdischarge device and permitting current to flow through the two mainelectrodes which allows the energy storage capacitor 153 to dischargethrough the blasting caps connected to the output terminals 190. If itis desired to eliminate manual firing of the blasting caps and to havethe blasting machine discharge the energy in the capacitor 153automatically when it has reached a predetermined energy level, thefiring switch 181 may be eliminated completely. ln this instance, assoon as voltage pulses are available from the pulse generator 5, thethree-electrode spark discharge device 180 would be triggered todischarge the energy in the capacitor 153 through the blasting caps (notshown) connected to the terminals 190.

OPERATION Referring now to FIG. 2, the circuit operates as follows: Whenswitch 9 is in the OFF position, resistor 154 removes the energy storedin capacitor 153. When switch 9 is closed, resistor 154 is removed fromthe circuit and current flows from the battery 140 through capacitor 130and through transistor 121, resistor 122 and resistor 123. Accordingly,a voltage is applied across the voltage divider network containingtransistor 121 and the voltage dividing network containing diode 110.Since there is a positive voltage applied across the emitter basecircuit of the transistor 121, the transistor 121 conducts permitting acurrent to flow through resistors 122 and 123 and through lead 124 tothe base of transistor 103 which is in the nonconducting state. When thecurrent to the base of transistor 103 is sufficient, transistor 103conducts (ON). When the transistor 103 conducts, current flows throughthe transformer primary winding 101 and transistor 103. With currentflowing to ground through the primary winding 101, transistor 121 beginsto return to the nonconductive (OFF) state as the base to emittercurrent of that transistor begins to decrease. Eventually transistor 121becomes nonconductive, removing the necessary base current to transistor103 which also becomes nonconductive (OFF). Once the transistor 131turns OFF, the electrical energy stored in the primary winding 101during the ON or conduction period of transistor 131 is removed ascurrent leaves the primary winding 131 and flows through diodes 104,106, 110 and resistors 111 and 112. This action also operates to backbias transistor 121 so that it remains in the nonconductive state.Further, since during this time the rate of change of current withrespect to time (di/dt) becomes sharply negative the voltage inducedacross the secondary winding 151 for this period also reverses and thesecondary winding 151 becomes a current source. Therefore, during thetime d/dt is negative, most of the energy stored in the primary windingof the transformer is transferred to the secondary winding 151 in amanner that allows the diode 152 to conduct and to supply energy to thecapacitor 153 and to supply energy to the capacitor 153 and to a load(not shown). Thus, electrical energy which is fed to the primary windingduring the conducting period of transistor 103 is transferred to thecapacitor 153 during the nonconducting period of transistor 103. Theentire action is cyclic for as the energy is removed from thetransformer the reverse bias on transistor 121 is removed allowingtransistors 121 and 103 to turn ON and repeat the entire operationagain. (About 800 to 2,000 Hz.)

As the energy stored in the capacitor reaches a predetermined level, thepulse generating circuit 5 begins generating trigger pulses. This occurswhen the spark gap discharge device 170 reaches its breakdown potential.To assure that the energy stored in the capacitor is above thepredetermined energy level but not in excess of a second and higherenergy level, a voltage regulator circuit 2 is utilized. This eliminatesexcessive energy levels that cause adverse operation of the blastingmachine.

Once the trigger pulses are present and the energy stored in thecapacitor is within a preferred range depressing the firing switch 181applies trigger pulses to transormers 182 which causes spark gap device180 to conduct, thereby allowing the energy in capacitor 153 todischarge into the blasting caps (not shown) attached to the outputs 190and detonate explosives.

ln one satisfactorily operable system, the blasting machine described inFIG. 2 was powered by 6 one and one-half volt D size batteries or onel2-volt Energizer battery No. S-121 and the circuit elements add thevalues or were of the types indicated below:

Capacitor 130 Capacitor Capacitor 177 3,300 microfarad, 30 Volts d.c.0.45 to 0.61 microfarad SKV 0.008 to 0.0l2 microfarad, 3.5KV

400 microfarad 2.5KV

0.025 to 0.03 microfarad SKV Capacitor 153 Capacitor 187 Resistor 1226.2 ohms, llW Resistor 123 33 ohms ll2W Resistor 111 100 ohms 2WResistor 112 1,000 ohms, l/2W Resistor 113 Resistor 154 10K ohms l/2W 3Kohms 10W Resistor 167 20K ohms 20W (2 in series) Resistor 163 2 ohms 20W(2 in parallel) Resistor 175 0.33 megohms 2W Resistor 173 l.36 megohms4W (2 in series) Resistor 171 500 ohms 10W Resistor 186 20 megohms 1WResistor 183 1K ohms 5W Resistor 189 10K ohms 10W Transistor 121Transistor 103 Diodes 0,102,104,106 Diode 152 Discharge Device 160 TypeMJE 341 Type 2N3055 Beta 20-35 GE Al4F Motorola MR 995A 2,200 volts d.c.(breakdown) Bendix Corp. Sidney, N.Y. Part No. l0-374l05-2l 2,000 voltsd.c. (breakdown) Bendix Corp. Sidney,N.Y. Part No. l0-37412l-l4Discharge Device Transformer 150 Transformer 182 Switch 9 and 181 Whilea preferred embodiment of the invention has been disclosed, it will beapparent to those skilled in the art that changes may be made to theinvention as set forth in the appended claims, and in some cases,certain features of the invention may be used to advantage withoutcorresponding use of other features. For example, different types ofsemi-conductors, or solid state control devices may be substituted forthe types illustrated. Accordingly, it is intended that the illustrativeand descriptive materials herein be used to illustrate the principles ofthe invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

l. A blasting machine comprising:

means for storing electrical energy;

means for supplying electrical energy to said energy storage means, saidmeans for supplying electrical energy comprising:

a source of electrical energy;

a transformer having a primary winding connected to said source and asecondary winding;

a first diode means and said electrical storage means connected togetherin series across said secondary winding to store energy generated by thecurrent flowing throughsaid primary winding;

a solid state switch oscillator connected to said source and saidtransformer to periodically interrupt current flow from said sourcethrough said prim ary winding, said oscillator including:

a first transistor having collector and emitter terminals in series withsaid primary winding, said transistor having alternate conductive and'nonconductive intervals to periodically interrupt the current flowingfrom said primary winding;

a first voltage divider network connected across said first transistorand said primary winding, said first voltage divider network includingsecond diode means connected to the junction between said primarywinding and said first transistor to direct current from said winding ina predetermined manner; and

a second voltage divider network connected across said source ofelectrical energy, said second voltage divider network including asecond transistor having alternate conductive and nonconductiveintervals to respectively control the conductive and nonconductiveintervals of said first transistor whereby the flow of current from saidsource to said primary winding is periodically interrupted causingcurrent to flow in an oscillatory manner through said primary winding.

means for producing a plurality of electrical pulses when said energystorage means has reached a first predetermined energy level;

switching means for receiving said pulses, said switching means operableto permit the discharge of said energy storage means only during thepresence of said pulses, whereby said energy storage means cannot bedischarged below said predetermined energy level; and

means for preventing said means for storing electrical energy fromexceeding a second predetermined energy level which is above said firstpredetermined energy level whereby said energy storage means isprevented from reaching energy levels above said second predeterminedenergy level.

2. A blasting machine as described in claim 1 wherein said means forpreventing said means for storing electrical energy from exceeding asecond predeter mined voltage level includes an electrical circuit whichcomprises:

a gaseous conductor connected in series to a resistor and a capacitor,said capacitor connected in parallel with a second resistor, saidelectrical circuit connected across said means for storing electricalenergy whereby when said means for storing elec trical energy reachessaid second predetermined energy level, said gaseous conductor conductsto prevent said means for storing electrical energy from exceeding saidsecond predetermined energy level.

3. The blasting machine as recited in claim l wherein the first voltagedividernetwork of said means for supplying electrical energy to saidenergy storage means comprises: .L

between said first transistor and said source of electrical energy.

4. A blasting machine as described in claim 3 wherein said means forpreventing said means for storing electrical energy from exceeding asecond predetermined voltage level includes an electrical circuit whichcomprises:

a gaseous conductor connected in series to a resistor and a capacitor,said capacitor connected in parallel with a second resistor, saidelectrical circuit connected across said means for storing electricalenergy whereby when said means for storing electrical energy reachessaid second predetermined energy level, said gaseous conductor conductsto prevent said means for storing electrical energy from exceeding saidsecond predetermined energy level.

S. A blasting machine which comprises:

means for storing electrical energy;

means for supplying electrical energy to said energy storage means, saidmeans for supplying electrical energy comprising:

a source of electrical energy;

a transformer having a primary winding connected to said source and asecondary winding;

a first diode means and said electrical energy storage means connectedtogether in series across said secondary winding to store energygenerated by the current flowing through said primary winding;

a solid state switch oscillator connected to said source and saidtransformer to periodically interrupt current flow from said sourcethrough said primary winding, said oscillator including:

a first transistor having collector and emitter terminals in series withsaid primary winding, said transistor having alternate conductive andnonconductive intervals to periodically interrupt the current flowingfrom said primary winding',

a first voltage divider network connected across said first transistorand said primary winding, said first voltage divider network includingsecond diode means connected to the junction between said primarywinding and said first transistor to direct current from said windingunidirectionally to said first voltage divider network; and

a second voltage divider network connected across said source ofelectrical energy, said second voltage divider network including asecond transistor having alternate conductive and nonconductiveintervals to respectively control the conductive and nonconductiveintervals of said first transistor whereby the flow of current from saidsource to said primary winding is periodically interrupted causingcurrent to flow in an oscillatory manner through said primary winding;

means for producing a plurality of electrical pulses when said energystorage means has reached a first predetermined energy level, said meansfor producing electrical pulses including a second normallynonconductive gaseous conductor which is rendered conductive when apredetermined voltage is applied thereto and a resistor capacitorcircuit in series with said second gaseous conductor so that when saidsecond gaseous conductor is rendered conductive, said capacitor lowersthe voltage applied to said second gaseous conductor below saidpredetermined value and said second gaseous conductor is renderednonconductive;

switching means for receiving said pulses, said switching means operableto permit the discharge of said energy storage means only during thepresence of said pulses, whereby said energy storage means cannot bedischarged below said predetermined energy level, said switching meansincluding a first normally nonconductive gaseous conductor in circuitrelationship with said pulse means, said first gaseous conductor beingrendered conductive upon receiving said pulses, whereby when pulses fromsaid pulse means are transmitted to said first gaseous conductor, saidfirst gaseous conductor is rendered conductive to permit said storagemeans to discharge and a switch connected between said first gaseous andsaid pulse means, said switch operable in the ON position to permitpassage of said pulses to said first gaseous conductor, whereby theenergy storage means is discharged only when said switch is in the ONposition and when said pulse means is producing pulses; and

means for preventing said means for storing electrical energy forexceeding a second predetermined energy level which is above said firstpredetermined energy level whereby said energy storage means isprevented from reaching energy levels above said second predeterminedenergy level.

6. A blasting machine as described in claim 5 wherein said means forpreventing said means for storing electrical energ mined voltage levecomprises:

,from exceeding a secor.id predeterincludes an electrical circuit whicha third gaseous conductor connected in series to a resistor and acapacitor, said capacitor connected in parallel with a second resistor,said electrical circuit connected across said means for storingelectrical energy whereby when said means for storing electrical energyreaches said predetermined energy level, said third gaseous conductorconducts to prevent said means for storing electrical energy fromexceeding said second predetermined energy level.

7. A blasting machine as recited in claim 5 wherein said first voltagedivider network of said means for supplying electrical energy to saidenergy storage means comprises:

wherein said means for preventing said means for storing electricalenergy from exceeding a second predetermined voltage level includes anelectrical circuit which comprises:

a third gaseous conductor connected in series to a resistor and acapacitor, said capacitor connected in parallel with a second resistor,said electrical circuit connected across said means for storingelectrical energy whereby when said means for storing electrical energyreaches said predetermined energy level, said third gaseous conductorconducts to prevent said means for storing electrical energy fromexceeding said second predetermined energy level.

1. A blasting machine comprising: means for storing electrical energy;means for supplying electrical energy to said energy storage means, saidmeans for supplying electrical energy comprising: a source of electricalenergy; a transformer having a primary winding connected to said sourceand a secondary winding; a first diode means and said electrical storagemeans connected together in series across said secondary winding tostore energy generated by the current flowing through said primarywinding; a solid state switch oscillator connected to said source andsaid transformer to periodically interrupt current flow from said sourcethrough said primary winding, said oscillator including: a firsttransistor having collector and emitter terminals in series with saidprimary winding, said transistor having alternate conductive andnonconductive intervals to periodically interrupt the current flowingfrom said primary winding; a first voltage divider network connectedacross said first transistor and said primary winding, said firstvoltage divider network including second diode means connected to thejunction between said primary winding and said first transistor todirect current from said winding in a predetermined manner; and a secondvoltage divider network connected across said source of electricalenergy, said second voltage divider network including a secondtransistor having alternate conductive and nonconductive intervals torespectively control the conductive and nonconductive intervals of saidfirst transistor whereby the flow of current from said source to saidprimary winding is periodically interrupted causing current to flow inan oscillatory manner through said primary winding. means for producinga plurality of electrical pulses when said energy storage means hasreached a first predetermined energy level; switching means forreceiving said pulses, said switching means operable to permit thedischarge of said energy storage means only during the presence of saidpulses, whereby said energy storage means cannot be discharged belowsaid predetermined energy level; and means for preventing said means forstoring electrical energy from exceeding a second predetermined energylevel which is above said first predetermined energy level whereby saidenergy storage means is prevented from reaching energy levels above saidsecond predetermined energy level.
 2. A blasting machine as described inclaim 1 wherein said means for preventing said means for storingelectrical energy from exceeding a second predetermined voltage levelincludes an electrical circuit which comprises: a gaseous conductorconnected in series to a resistor and a capacitor, said capacitorconnected in parallel with a second resistor, said electrical circuitconnected across said means for storing electrical energy whereby whensaid means for storing electrical enerGy reaches said secondpredetermined energy level, said gaseous conductor conducts to preventsaid means for storing electrical energy from exceeding said secondpredetermined energy level.
 3. The blasting machine as recited in claim1 wherein the first voltage divider network of said means for supplyingelectrical energy to said energy storage means comprises: a diode havinga first terminal connected to the junction between said primary windingand said source of electrical energy and a second terminal connected tothe base of said second transistor; a first resistor in series with thesecond terminal of said diode; a second resistor in series with saidfirst resistor, and a third resistor in series with said second resistorand having one terminal connected to the junction between said firsttransistor and said source of electrical energy.
 4. A blasting machineas described in claim 3 wherein said means for preventing said means forstoring electrical energy from exceeding a second predetermined voltagelevel includes an electrical circuit which comprises: a gaseousconductor connected in series to a resistor and a capacitor, saidcapacitor connected in parallel with a second resistor, said electricalcircuit connected across said means for storing electrical energywhereby when said means for storing electrical energy reaches saidsecond predetermined energy level, said gaseous conductor conducts toprevent said means for storing electrical energy from exceeding saidsecond predetermined energy level.
 5. A blasting machine whichcomprises: means for storing electrical energy; means for supplyingelectrical energy to said energy storage means, said means for supplyingelectrical energy comprising: a source of electrical energy; atransformer having a primary winding connected to said source and asecondary winding; a first diode means and said electrical energystorage means connected together in series across said secondary windingto store energy generated by the current flowing through said primarywinding; a solid state switch oscillator connected to said source andsaid transformer to periodically interrupt current flow from said sourcethrough said primary winding, said oscillator including: a firsttransistor having collector and emitter terminals in series with saidprimary winding, said transistor having alternate conductive andnonconductive intervals to periodically interrupt the current flowingfrom said primary winding; a first voltage divider network connectedacross said first transistor and said primary winding, said firstvoltage divider network including second diode means connected to thejunction between said primary winding and said first transistor todirect current from said winding unidirectionally to said first voltagedivider network; and a second voltage divider network connected acrosssaid source of electrical energy, said second voltage divider networkincluding a second transistor having alternate conductive andnonconductive intervals to respectively control the conductive andnonconductive intervals of said first transistor whereby the flow ofcurrent from said source to said primary winding is periodicallyinterrupted causing current to flow in an oscillatory manner throughsaid primary winding; means for producing a plurality of electricalpulses when said energy storage means has reached a first predeterminedenergy level, said means for producing electrical pulses including asecond normally nonconductive gaseous conductor which is renderedconductive when a predetermined voltage is applied thereto and aresistor capacitor circuit in series with said second gaseous conductorso that when said second gaseous conductor is rendered conductive, saidcapacitor lowers the voltage applied to said second gaseous conductorbelow said predetermined value and said second gaseous conductor isrendered nonconductive; switching means for receiving said pulses, saidswitchinG means operable to permit the discharge of said energy storagemeans only during the presence of said pulses, whereby said energystorage means cannot be discharged below said predetermined energylevel, said switching means including a first normally nonconductivegaseous conductor in circuit relationship with said pulse means, saidfirst gaseous conductor being rendered conductive upon receiving saidpulses, whereby when pulses from said pulse means are transmitted tosaid first gaseous conductor, said first gaseous conductor is renderedconductive to permit said storage means to discharge and a switchconnected between said first gaseous and said pulse means, said switchoperable in the ON position to permit passage of said pulses to saidfirst gaseous conductor, whereby the energy storage means is dischargedonly when said switch is in the ON position and when said pulse means isproducing pulses; and means for preventing said means for storingelectrical energy for exceeding a second predetermined energy levelwhich is above said first predetermined energy level whereby said energystorage means is prevented from reaching energy levels above said secondpredetermined energy level.
 6. A blasting machine as described in claim5 wherein said means for preventing said means for storing electricalenergy from exceeding a second predetermined voltage level includes anelectrical circuit which comprises: a third gaseous conductor connectedin series to a resistor and a capacitor, said capacitor connected inparallel with a second resistor, said electrical circuit connectedacross said means for storing electrical energy whereby when said meansfor storing electrical energy reaches said predetermined energy level,said third gaseous conductor conducts to prevent said means for storingelectrical energy from exceeding said second predetermined energy level.7. A blasting machine as recited in claim 5 wherein said first voltagedivider network of said means for supplying electrical energy to saidenergy storage means comprises: a diode having a first terminalconnected to the junction between said primary winding and said sourceof electrical energy and a second terminal connected to the base of saidsecond transistor; a first resistor in series with the second terminalof said diode; a second resistor in series with said first resistor; anda third resistor in series with said second resistor and having oneterminal connected to the junction between said first transistor andsaid source of electrical energy.
 8. A blasting machine as described inclaim 7 wherein said means for preventing said means for storingelectrical energy from exceeding a second predetermined voltage levelincludes an electrical circuit which comprises: a third gaseousconductor connected in series to a resistor and a capacitor, saidcapacitor connected in parallel with a second resistor, said electricalcircuit connected across said means for storing electrical energywhereby when said means for storing electrical energy reaches saidpredetermined energy level, said third gaseous conductor conducts toprevent said means for storing electrical energy from exceeding saidsecond predetermined energy level.